Begin by cutting the lemons in half. Squeeze the juice into a small bowl, making sure to remove any seeds. Set the juice aside for later.
In a cocktail shaker or a tall glass, combine the mint leaves and sugar. Use a muddler or the back of a spoon to gently crush the mint leaves. This step releases the mint’s essential oils and combines it with the sugar, enhancing the drink’s flavor.
Pour the freshly squeezed lemon juice into the shaker or glass with the mint and sugar mixture. Stir well to dissolve the sugar and ensure the flavors are evenly distributed.
Fill two serving glasses with ice cubes. Pour the mint and lemon mixture over the ice in each glass.
Top each glass with sparkling water or soda, filling it to the brim. Stir gently to combine the ingredients, taking care not to lose the fizz.
Add a lemon slice and a sprig of mint to each glass for a polished, restaurant-quality look. Serve immediately and enjoy the refreshing burst of flavor!